* Increased efficiency of reading input stream
* Huffman decoding re-expressed in assembler.
* IDCT code tuned a bit further
* motion compensation routines speeded up (this is the biggy because the Iyonix has a fast CPU core but a relatively slow memory interface)
* optimised a bit more of the CPU-intensive core of AC3 decoding

So, there's no longer any need to play from RAM disc It's playing at about 50% real-time (12.5fps) on average from HD, when all video & audio is decoded and rendered, which means that by dint of dropping B-type pictures DVDs are now comfortably watchable and the audio rarely breaks up.

I had a look at the profiling info playing from DVD and, with all the other stages being much faster, I'm now wasting about 25-30% of the CPU time just fetching the data from the disc (still PIO, you see)..... so, I guess it's about time that I got the DMA ATAPI stuff working & polished off! (That's why you have to play from HD at the moment to get good playback, not because the HD is intrinsically faster. In fact we only need to read about 2-3MB/s.)

Having done all this work tuning my MPEG decoder - on a processor that, frankly, was never intended for playing video - we'll be looking for other uses. Suggestions on the back of a postcard, please